1. Field of the Invention
This invention relates to a process for producing a silicon-containing polyamic acid and also a process for producing a crosslinked silicon-containing polyimide.
2. Description of the Prior Art
Polyimide resins have so far been widely used for protecting materials, insulating materials and adhesives in the field of electronic equipment or films, structural materials, etc. mainly in the aspect of heat resistance.
Further, a process of making the above resins composite with other inorganic materials and using the resulting compositions as heat-resistant films, coating agents or adhesives has also been employed. In this case, if the inorganic materials are silicon-containing compounds such as glass, copolymers thereof with silicon compounds have often been proposed as a means for improving their adhesion. For example, Japanese patent application laid-open Nos. Sho 57-143328/1982, Sho 58-7473/1984 and Sho 58-13631/1984 propose a technique wherein a polyimide siloxane copolymer is prepared using a polyimide precursor obtained by replacing a portion of the raw material diamine component by a polysiloxane terminated with diamines at both ends thereof. In this case, however, although adhesion improvement to a certain extent is observed, a problem has been raised that the polymerization degree decreases with increase in the siloxane content in the copolymer, to reduce the coating-formability.
Further, Japanese patent publication Nos. Sho 58-18372/1983, Sho 58-32162/1983 and Sho 58-32163/1983 disclose a process wherein a suitable carboxylic acid derivative such as tetracarboxylic acid dianhydride is reacted with a diamine, to form a polyamidecarboxylic acid having a terminal group such as an acid anhydrides. One mol of this polyamidecarboxylic acid is reacted with at least two mols of an aminosilicon compound at -20.degree. C. to +50.degree. C., to obtain a silicon-containing polyamidecarboxylic acid prepolymer (a precursor), which is not imidized, or is imidized (chemically cyclized) under mild conditions (low temperature, preferably 50.degree. C. or lower, particularly -20.degree. C. to +25.degree. C.) in the presence of a dehydrating agent to form an organic silicon-modified polyimide precursor. The former unimidized precursor or the latter polyimide precursor is heated (baked) in the form of a solution in the presence or absence of a silane diol or a siloxane diol to effect completion of imidization and also cross-linking, to thereby obtain a polyimide-siloxane. However, according to such a process, adhesion to silicon compounds is improved to a certain extent, but adhesion to e.g. aluminum is insufficient. Further, laminated coatings have often been practically formed as follows: a polymer solution is applied onto an object to be adhered, followed by baking it to form a coating, thereafter, again applying the same polymer solution onto the above coating and baking it to form a coating onto the former coating (such an adhesion will hereinafter be often referred to as "adhesion between coatings"). However, adhesion in such a case has been unsatisfactory.
Further, Japanese patent application laid-open No. Sho 57-212230/1982 discloses a molded product of a polyimide resin composition obtained by heating a polymer composition consisting of 99.9 to 70.0% by weight of a polyamic acid or a polyamide-amic acid and 0.1 to 30.0% by weight of a specified organic silicon compound. However, in this case, too, improvement in adhesion to silicon compounds is observed to a certain extent, but the above-mentioned adhesion between coatings has not been satisfactory.
As described above, the prior art has raised various problems. Thus, development has been desired of a polyimide resin or a precursor affording such a polyimide resin, having a considerable extent of heat resistance as adhesives or resins for multilayer laminated composite materials, and also having a good adhesion onto inorganic materials or metals and also a good adhesion of resins to each other.
The object of the present invention is to provide a means to solve the above-mentioned problems of the prior art and satisfying the above-mentioned desire.